1. Field of the Invention
The present invention relates to liquid metal-filled balloon catheters suitable for application in hyperthermia and ablation, and specifically to the method of use of balloon catheters in endometrial ablation.
2. Related Art
Medical electrical heating catheters are used for tissue heating, typically in oncological hyperthermia (e.g., Chou et al., U.S. Pat. No. 4,865,047), in prostatic hyperplasis (e.g., Turner el al., U.S. Pat. No. 4,967,765) and also in thermal ablation of tissue exemplified by destruction of cardiac arrhythmogenic tissue (e.g., Langberg, U.S. Pat. No. 4,945,912). Electrical heating is accomplished by applying electrical power through a metal electrode equipped applicator to tissue. A wide variety of styles of electrodes for applicators exists, adapted to the geometry of the tissue to be heated and to the frequency of the applied electrical field which can range from DC pulses to microwaves. Generically, heating by Electro-Magnetic Radiation (EMR) is characterized by providing a metallic electrode serving as a conductor to guide the penetration of the EMR field into the tissue.
Typically, EMR applicators have rigid metallic electrodes, which are adequate for many applications but not when the geometry of the organ to be heated is complex, or the geometry of the organ varies greatly from patient to patient, or the organ exhibits plasticity requiring application of a very uniform pressure during the procedure. The required size of the rigid electrode may also cause difficulty when inserting the device. Geddes et al. in U.S. Pat. No. 4,979,948 proposes a radio-frequency (RF) ablation catheter using an liquid electrolyte-filled balloon, which overcomes the inconvenience of a rigid electrode. The current-emitting electrode of Geddes heats primarily the electrolyte inside the balloon because the conductivity and the dielectric constant of tissue is typically of the same order of magnitude as an electrolyte solution. Heating of the tissue is done primarily by heat conduction from a hot balloon which could be accomplished by an ordinary heater. The objective of the RF heating is to let the RF field in the tissue do the heating which requires much higher conductivity of the fluid in the balloon.
A principal feature distinguishing the present invention from prior art devices is the use of a liquid metal, and specifically, a gallium-filled balloon to serve as an applicator of an electrode catheter. The liquid metal-filled balloon applicator has the advantages of fluidity and so is inherently capable of a small cross section for easy insertion and subsequent expansion in conformity to a complex and variable geometry of intracavitary space. Metallic conductivity prevents any electric fields to form inside liquid metal-filled balloon and forces electric fields to the surface where they interact with the tissue.
EMR heating catheters with rigid applicators are used for endometrial ablation of the uterus, as reported by Phipps et al. in Obstetrics & Gynecology. Vol. 76, No. 5, Part 1, November: 876-881, 1990 and also in European Patent Application No. 0 407 057 A1 by Stanley B. Field and Jeffrey H. Phipps ("Phipps et al"). This catheter is much simpler to use than the hysteroscopic techniques now frequently employed for endometrial ablation. Phipps et al reports use of a straight and a curved applicator probe. The disadvantage of the straight probe applicator, as reported by Phipps et al, is that because of the shape of the uterus (see FIG. 2) the cornua is not exposed to adequate electric field heating, leading to incomplete endometrial ablation in the cornua region. A curved probe tip which fits into the cornua requires 360 degree rotation during the procedure. The curvature of the tip is quite critical and there is delicate compromise between good apposition of the cornua and safety concerns relating to intrauterine injury due to the required rotation of the curved probe.
Another feature of the present invention is the application of balloon method for performance of endometrial ablation.